How to heal a blister without popping?

Leave it alone: A simple blister, that is one that is not in an area that is constantly under pressure, such as on the buttock, will gradually subside in size and begin to heal from within. Popping it, though tempting, is only cosmetic, and if you are in any way immunocompromised puts you at risk of infection. So leave it alone, and if it is sore or red, apply a little topical Bacitracin to keep the skin soft.

Protect it: An unpopped blister represents a closed sterile environment. Yes on occasion one can become infected then it is time to open it, however the risk of infection in a dressed open wound is still higher than that of an intact blister. The blister will gradually resolve with time.